Neuropeptide modulation of biogenic amine function and aggression in a crustacean. The long-term goal of this project is to understand the mechanisms that control aggressive behavior in an invertebrate model and how the underlying neural circuits are modulated in response to signals from the organism's internal and external environment. The specific goal is to understand how the effects serotonin (5-HT) and octopamine (OA) have on aggressive behavior of dominant and submissive freshwater prawns are modulated by neuroactive peptides. Adult male prawns develop through three morphotypes, corresponding with the animal's status in a dominance hierarchy. The typical behaviors of each morphotype vary quite markedly in aggression, territoriality and attitude towards females. While other crustacean models such as the crab, crayfish and lobster, have been used extensively to study interactive behaviors, the prawn offers the advantage of marked differences in characteristic behaviors of each morphotype and the fact that the position each animal assumes in the hierarchy of dominance is first determined by its morphotype rather than by its body size. There is ample evidence linking biogenic amines to behaviors associated with the establishment of social hierarchies in both vertebrates and invertebrates, but the specific mechanisms by which these amines act remain largely unknown. Serotonin and OA have been shown to play an important role in modulating aggression and fighting behavior in crustaceans, including the prawn, but the evidence suggests that they are not the sole determinant elements. Aggression and fighting behavior can vary depending on circumstances such as availability of food, shelter and partners for reproduction, level of exposure to contaminants, light/dark cycles, health status, etc. The primary mechanisms that produce aggressive behavior are likely to be susceptible to diverse sources of modulation that allow the organism to adjust its responses to the prevailing circumstances. We are interested in studying the role played by neuroactive peptides in modulating the actions of biogenic amines and how this modulation results in changes in aggressive behaviors in the prawn. The specific scientific aims of the proposed research are to: (1) Characterize the role played by proctolin, FMRFamide, SIFamide and newly identified prawn neuropeptides in modulating natural aggressive behaviors of the prawn male morphotypes and aggressive behaviors induced by injection of 5-HT and OA;(2) Characterize the central nervous system (CNS) distribution of these neuropeptides in the prawn morphotypes and determine how it relates with those of 5-HT and OA;and (3) Quantify the relative amounts of these neuropeptides in the circulating hemolymph of the prawn morphotypes. To achieve these aims, we will use techniques of behavioral observation and quantitation before and after injections of agents of interest, CNS dissection, immunohistochemistry, confocal microscopy, hemolymph sampling and quantitative mass spectrometry.